Humans looking for a bit of romance might whisper sweet nothings in the ears of their prospective partners. The white bellbird, a small Amazonian species with some serious vocal power, opts for a less subtle approach. When a desirable female approaches, the male bellbird whips its head around and screams a shattering note in her direction—a song that is, in fact, the loudest of any bird, according to a new study in Current Biology.
White bellbirds fly about in mountainous regions of the Brazilian Amazon, emitting a strange, tinny call that is impossible to miss. “You can hear them from a mile away,” Mario Cohn-Haft, study co-author and curator of birds at the National Institute of Amazonian Research in Brazil, tells Cara Giaimo of the New York Times.
While examining a white bellbird specimen during a 2017 trip to the region, Cohn-Haft was struck by what he describes as the bird’s “really ripped, washboard stomach.” He suspected that rock-hard abs help bellbirds project their song at top volumes, but just how loud the species could get was a question that had not yet been answered. So Cohn-Haft and Jeffrey Podos, the first author of the study, set out to measure the call of the white bellbird.
Recording wild bird songs can be a difficult undertaking—tools often need to be carefully calibrated, but the researchers were able to rely on high-quality sound recorders and a “new generation” sound level meter that takes highly precise measurements of sound pressure, as Podos tells Discover's Leslie Nemo.
"This allows us to see how amplitude changes and peaks within individual singing events,” Podos explains.
The white bellbirds belted out two song types. The first was relatively common and could reach around 116 decibels. (Human voices, by way of comparison, clock in at about 60 decibels. The second song, which was emitted in the presence of females, reached wincing levels of around 125 decibels.
That volume, Podos notes in an interview with Giaimo, rivals “the amplitude of a pile driver.” It is also more than nine decibels louder than the call of the screaming piha, a white bellbird relative that previously held the title for the world’s loudest bird song. Podos tells Adam Vaughan of New Scientist that even louder bird species likely exist, the strength of their calls still waiting to be measured. But the booming song of the white bellbird is still impressive because the species is quite small, weighing only about half a pound.
The birds’ gaping beaks, which they use to gulp down berries, might help boost their powerful calls, as do their strong stomach muscles. A trade-off seems to be at work, however; the researchers found that as the birds’ songs grew more intense, their calls also got shorter, probably because white bellbirds’ respiratory systems have a finite ability to generate sound.
In this loud little creature, the researchers see a prime example of sexual selection, or the evolution of extreme traits that give animals a leg up as they compete for mates—like peacocks’ showy tails and birds’ of paradise wild dance moves. A blaring call could help summon female bellbirds over long distances, and females seem to find loud songs attractive, given how the males behaved when a prospective mate joined them on their perches.
“In this context, the male first adopted a head-down/ tail-down posture, back towards the female, wattle fully distended,” the study authors explain. “He then sang only his higher amplitude ... song, swiveling dramatically midsong to face the female head-on for the song’s second note.”
But the researchers were admittedly puzzled by how close females would get as males shrieked out their highest amplitude song—so close, in fact, that it seemed their hearing might be damaged. "Maybe they are trying to assess males up close,” Podos theorizes, “though at the risk of some damage to their hearing systems."
Moving forward, the researchers hope to conduct further investigations into the physical features that let bellbirds produce such loud calls—and tolerate listening to them. It’s an important area of study because, as Podos notes, bird communication is "the glue that holds [their] societies together."